Transmission of sound currents



jan. 26, 1937. E, s LAN5| NG 2,068,685

TRANSMISSION OF SOUND CURRENTS Filed Aug. 22, 1950 v INVENTOR. Bow/wo Lmms/nfs.

BY M im;

Patented Jan. 26, 1937 UNETED STATE .ear

FFCE

Edward S. Lansing, Detroit, Mich., assigner of one-half to Osborne A.Bryan, Detroit, Mich.

Application August 22, 1930, Seria! No. 477,060

10 Claims.

This invention relates to the transmission of sound currents, and has todo particularly with the dividing and amplifying of sound currents inrecording and reproducing devices of various types.

Heretofore in the reproduction of sound by radio receiving sets andsimilar sound reproducing devices a very serious problem has beenpresentedin obtaining a reproduction which in any way simulates theoriginal source of sound. The difficulty of reproducing and amplifyinglow frequency notes is well recognized and in modern reproducing unitswherein the sound waves are transmitted by alternating electric currentsattempts have been made to bring out these low frequency notes byproviding suiiicient power to give greater amplification. However, thepower required to properly sound the low notes in dynamic loud speakersand the like is much great- 20 er than the power required for soundingthe high frequency notes. with the result that the high frequency notesare appreciably distorted.

More' recently attempts have been made to obviate this distortion byattempting to accentuate or emphasize either the bass or treble notes,but the difliculty in all such attempts has been that thecharacteristics and quality of the original musical sound are changed.In other Words, these attempts to emphasize either the bass or treblenotes are generally based on the shifting of the pitch.

It is known that a condenser will pass alternating currents of highfrequency and bypass a large percentage of the'low frequency currentswhile contrariwise a choke coil will absorb or pass alternating currentsof low frequency and shut off or bypass those of high frequency. Theabove principles have been utilized experimentally in attempting toobtain separation of the low and high frequency notes and attempts havealso been made experimentally to amplify some frequencies that have beenseparated to control the relative intensity given different frequencies.However, so far as I am aware, these latter attempts have not beenentirely successful, one reason being apparently because complete clearseparation of high and low frequencies Was not obtained, and anotherapparent reason being ,because very little amplification was given suchfrequencies as were separated.

It is the object of the present invention to provide means placed aheadof any standard reproducing and/or amplifying device for positivelydividing the transmitted musical tones transmitting s aidpositivelydivided frequencies as true and clear duplicates of the original sourceof sound and then positively amplifying the divided and transmittedfrequencies so as to obtain any desired individual amplification of thedivided high and low frequencies. The invention resides both in themethod for obtaining this individual division and amplincation and thenovel hook-up for making this method possible.

Specific features of my invention reside in the use of a plurality oftransformers, preferably of varying ratios, in combination with a novelmanner of connecting said transformers in parallel to a'condenser. Otherfeatures reside in the manner of connecting transformers to eliminateany sound connection therebetween, the manner of arranging a choke coilrelative to the high frequency transformer and the manner of connectingthe B current supply for the detector so as to eliminate all muddinessin the high frequency transformer. Other features embody the use of anovel electrical balancing network for the transformers to insurepositive amplification of approximately one stage and the individualcontrol of each transformer output with a variable resistance center tapconnected to ground. Other novel features will be more clearly broughtout in the specification and claims.

In the drawing:

Fig. l is a schematic layout of one manner of connecting my dividing andamplifying unit in between a standard detector or pick up and a standardamplifier.

Fig. 2 represents a diagrammatic wiring diagram of the preferredarrangement of my novel dividing and amplifying system.

Fig. 3 is a diagrammatic layout similar to Fig. 2 but illustrating asystem giving more complete control in that it separates the frequencyrange into three or more divisions.

In explaining the method of operation of my novel hook-up, the same willbe preferably shown and described as embodied in a typical standardradio receiving unit and the relative arrangement of parts is bestillustrated in the schematic layout of Fig. 1. Here my unit, which Iwill call a dividing and amplifying unit, is shown as at i connectedbetween the detector or pick up unit 2 and a standard amplifier unit 3.The unit I is shown in Fig. 1 in the manner of a now chart measured inintensity, the sound current being shown entering the unit at a with thestandard intensity. The high and low frequencies are positively dividedas at b and c and these divided frequencies may then be amplied orregulated to any desired amount; in Fig. 1 the high frequency tones arebeing only slightly amplified as at d while the loW frequency tones areamplified to a greater extent .as at e. The clear and individuallyamplified high and low frequencies are then joined together in one bandas at f when they are fed into the standard amplifier 3l correctlymodified as to relative intensity and at the same time being a trueduplicate .as to quality and pitch of the original source of sound.

The method of positively dividing and individually regulating andamplifying the divided sound Waves may be best understood by describingthe diagram as shown in Fig- 2. For general use I preferably use twotransformers 4 and 5, the transformer l preferably having a ratio of31/2 to l and the transformer 5 having a ratio of 31/2 to 1/2. Anystandard detector or pick up device 2 is directly connected to theterminals 5 on the primary of the rst transformerll. The other terminal'I of the primary is connected by means of the Wire 8 to a terminal 9 towhich terminal is connected the B supply.

It will thus be obvious that the transformers l and 5 are connected inparallel and there is no sound connection between the terminal 'I of thetransformer Il and the terminal IIJ of the primary of transformer 5. Itwill also be obvious that the B current Will be fed through the Wire 3so as to be completely-bypassed around the transformer 5 with the resultthat the B current can be fed only through the primary of thetransformer l and then to the detector. This latter feature is veryimportant as will be presently pointed out. The transformers d and 5 areconnected in parallel with one another through a .l mfd. condenser. 'Ihehigh frequency sound currents from the detector 2 will readily passthrough the condenser II, and the majority of the low frequency soundwaves will be deflected so they will pass through the primary of thetransformer 4I, this transformer becoming a low frequency transformer.

In the preferred arrangement .all of the frequencies are dividedapproximately in the center with the result that practically all of thesound waves having a frequency which places them below the center of themusical scale will be transmitted to the primary of the transformer d.As'the terminal 'I of the primary does not have a sound connection withthe second transformer 5, it will be obvious that there Will be nostrays transmitted from the primary of the transformer 4l to the primaryof the transformer 5. Thus the division of the 10W frequency tones iscomplete.

The notes of high frequency will pass through the condenser II and Whatfevv low frequency currents should pass through the condenser will beabsorbed by a choke coil I2. Thus by the use of a parallel connectedcondenser, a choke coil I2 and the bypassing of the wire 8 around thehigh frequency transformer, it Will be obvious that only the trueundistorted high frequency currents will be passed through the primaryof the transformer 5.

I believe that the reason for obtaining my markedly better results Withtransformers of different ratios is because the low frequency notesrequire greater amplification. Possibly there may be other reasons forthis result but the fact remains that better results are obtained byusing transformers of a different ratio and preferably of the ratioindicated. I find that because of the three means utilized for keepingthe low frequency currents out of the transformer 5 and because of theby-passing of the B current that all muddness in the high frequencytransformer 5 is eliminated. Because I have eliminated any soundconnection between the transformers better low frequency quality isobtained because I have eliminated the possibility of any high frequencycurrents or electrical strays breaking back into the 10W frequencytransformer.

A .01 mfd. condenser I3 is connected across the terminals I4 and I5 ofthe secondary of the transformer '4 to filter out any possible highfrequency notes that may pass through the secondary and any suchbypassed high frequency notes are conducted to the ground of thevariable re sistance I6. Not only does this variable resistance I5control the amplifying of the low frequency notes b'ut the connecting ofthe same with the ground is found to give very good results. A similarvariable resistance center tap I1 is connected across the terminals ofthe secondary I8 of the high frequency transformer to obtain adjustableamplification of the high frequency notes. I consider that thisadjustment of the high frequency tones is one of the most importantelements in the present system and contributes materially in the finalresults obtained. It Will thus be seen that any combination of the highfrequency and low frequency tones may be obtained by varying the powerintensity or amplification of each individual transformer.

In transmitting and combining the separately controlled high and lowfrequencies the secondary of the transformer 4 is connected directly tothe grid of a 27 or 20l-A tube I9, and the secondary I8 of the highfrequency transformer 5 connected directly to the grid of a similar tubeZtl. If the plates o-f these tubes Were tied together at this point itWill be obvious that there is no appreciable gain. I have discoveredthat if the plates are each connected to a B supply ZI through a 100,000ohm fixed resistance and then connected together thereto to separatecondensers 22 and 23, of preferably l mfd. capacity, I get a gain ofsubstantially one stage. The properly amplified individual soundcurrents are thus. combined in the proper phased balance and from thispoint may be fed into a standard audio amplifier to be amplied for usein the loud speaker. It will be obvious that because of the inherentamplication in my novel dividing and amplifying unit that the amplifyingeiciency of the standard amplifier may be materially increased, thuspermitting in many cases the discontinuance of the standard first stageof audio entirely.

In Fig. 3, I have illustrated a modification of my system as adaptedespecially for theatres and providing accurate acoustical balancetherefor.

through a single channel, substantially complete- 7,5

ly separating the combined sound currents into a plurality of componentparts maintaining said division and amplifying said parts individuallythrough a variable range and reproducing the sound currents through asingle channel amplifier and single speaker with their component partsof unequal frequency ranges.

2. The method of dividing and amplifying sound currents transmittedthrough a single channel, which comprises transmitting sound currents ofall the created frequencies from a common source through a singlechannel, separating the combined sound currents into a plurality ofcomponent parts, one of said parts being composed of currents ofrelatively low frequencies and another of relatively high frequencies,changing the volume of one frequency relative to the other, maintainingthe relatively high frequency component at its fixed volume andmaintaining the relatively low frequency component at its fixed volume,amplifying and then reproducing said sound currents through a singlechannel amplifier and single speaker at their relatively fixed values.

3. The method of dividing and amplifying alternating current soundfrequencies transmitted through a single channel which consists intransmitting sound currents of all the created frequencies from a commonsource through a single channel, separating the combined frequenciesinto a plurality of components, changing the relative volume of saidcomponents, individually controlling the frequency range of theseparated components, individually maintaining controlled range of eachcomponent, combining the components in phase with each other, and thenamplifying before reproduction.

4. In a sound frequency dividing and amplifying system of the classdescribed the combination "of high and low frequency transformers ofdifferent ratios having their primaries connected together in parallelthrough a condenser of a value adapted to pass substantially all of thehigh frequency currents, a choke in parallel with the primary of thehigh frequency transformer, the loW frequency transformer having acondenser bypass across the secondary, frequency range control meansconnected in parallel across the secondaries of each transformer, andvalves for maintaining the separated frequency ranges before combining,and means for amplifying the combined frequencies before reproduction.

5. In a sound frequency dividing and amplifying system of the classdescribed the combination of high and low frequency transformers havingtheir primaries connected together in parallel through a condenser of avalue adapted to pass substantially all of the high frequency currents,a choke in parallel with the primary of the high frequency transformer,the 10W frequency transformer having a grounded variable center tapcondenser bypass across the secondary, and a resistance connected inparallel with said condenser and said secondary, the secondaries of saidtransformers being completely separated, and a fixed resistance andcondensers combining the separate leads from the secondaries.

6. In a sound frequency dividing and amplifying system of the classdescribed, the combination of high and low frequency transformers havingtheir primaries connected together in parallel through a condenser of avalue adapted to pass substantially all of the high frequency currents,a choke in parallel with the primary of the high frequency transformer,the low frequency transformer having a condenser bypass across thesecondary, resistances for controlling the individual frequency rangesconnected in parallel across each transformer and having a groundedvariable center tap, the secondaries of said transformers beingcompletely separated, and a xed resistance and condensers combining theseparate leads from the secondaries.

7. A device for controlling the amplification of individual frequencycurrents comprising a plurality of transformers of different ratios,means for separating and feeding currents of different frequencies totransformers of predetermined value, means for supplying B current toone transformer only, means for variably and individually controllingthe range of the sound frequencies transmitted by each transformer,valves separately connected to the secondaries of each transformer formaintaining each frequency range, a resistance coupling for combiningthe separate maintained frequencies, and means for amplifying thecombined frequencies before reproduction.

8. A device for controlling the amplification of individual frequencycurrents comprising a plurality of transformers of different ratios,means including a condenser in parallel with one secondary, a choke inparallel with one primary for separating and feeding currents ofdifferent frequencies to predetermined transformers, means for variablycontrolling the range of the sound frequencies transmitted by eachtransformer, the secondaries of said transformers being completelyseparated, and a fixed resistance and condensers combining the separateleads from the secondaries.

9. A device for controlling the amplification of individual frequencycurrents comprising a plurality of parallel connected transformers ofdifferent ratios, means including a condenser in parallel with onesecondary, a choke in parallel with one primary for separating andfeeding currents of different frequencies to predetermined transformers,means for variably and individually controlling the range of the soundfrequencies by each transformer, valves separately connected to thesecondaries of each transformer for maintaining each frequency range, aresistance coupling for combining the separate maintained frequencies,and means for amplifying the combined frequencies before reproduction.

10. In a sound frequency dividing and amplifying system of the classdescribed, the combination of high and loW frequency transformersconnected together in parallel to permit passing of sound currents, thelovv frequency transformer having a condenser by-pass across thesecondary, a variable resistance connected in parallel with saidcondenser and low frequency transformer and a separate resistanceconnected in parallel with said high frequency transformer for variablycontrolling the range of sound frequencies transmitted by eachtransformer, reproducing means, means combining said frequency ranges,and amplifying means between the combining and reproducing means.

EDWARD S. LANSING.

